The game was made with AGS (Adventure Game Studio) so that's a limitation of that software. I think you'll find that most indie adventure games similarly will only run in lower resolutions, for example the Wadjet Eye stuff. RPG Maker is a similar situation.

I do think it would be nice if there were easy to use, affordable software out there for creating much more high resolution adventure games (and RPGs) too, but for now those resolutions are the limitations of the tools that are available. This game in particular I think has exceptional artwork and it would have been nice to have it in HD.

That being said, I play it in full screen myself and I think it works out really well. I never feel like it seems pixelated or low res like some of the other AGS made games can tend to look so I think the developers of this game did a really good job with the tools they had to work with making the game look good.

I'm not sure AGS actually enforces a low resolution. Some of the newer ones (such as Blackwell Deception) are higher res (albeit not super high). The Mage's Initiation project is apparently adding wide screen support to the engine.

There is also Visionaire Studio, quite a cheap adventure game engine most popularly used in the super high res games from Daedalic Entertainment.

Oh I see, I ended up buying the full game from their homepage, and have been playing for a while now. I have to say the game is truly excellent. It's a bit shame though that AGS has all these technical limitations.

Hopefully AGS will be updated in the future. I'm liking this game so much, that I would even like to see it remade in true HD on a more graphically advanced engine. But I guess this was not done in the first place because of cost/time constraints (but hey I know I would back a Kickstarter ;))